Evacuated container



June 24.- 1924. 1,498,908

' c. G. FINK' EVACUATED CONTAINER Filed Jan. 23, 1915 Witnesses Inventor-z Y Colin efink Patented June 24, 1924.

v UNITED STATES PATENT OFFICE.

. OOLIN Gu/FINK, ORANGE, NEW JERSEY, ASSIGNOR'TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

EVACUATED Application illed .Tanuary 23, 915. Serial No. 4,048.

To all whom it may concern: 4

Be. it known that I, COLIN G. FINK, a citizen of the United States, residing at East vOrange,.county .of Essex, State'of ew J er- 5 sey, have invented certain new and useful Improvements in Evacuated Containers, of

which the following is a' specification. This application is ip part a'continuation of my prior application, Serial No.- 703,801, .filed June 15, 1912. I v My invention relates to seals for leadingin conductors'for incandescent lamps, gas

,electric'lamps, mercury rectifiers and apparatus of a similar nature in which an envelope of glass or vitreous material is used andjn which it is necessar to provide means for conducting electrica energyv from a power circuit to conductors within the space enclos ed by the envelope. .2 1 In orderto make a seal for such apparatus which will be gas-tight, the leading-in conductor used should preferably have a coefficient of expansion which does not differ greatly from that of the material of the envelope. It is also necessary that there shall be a certain aflinity between the material of the envelope? when in a-plastic or partially liquid condition, and the surface 'of'the conductor, by reason of which there will be a tendency for the tvro to. stick together. .This property is usually spoken of as a wetting-of the conductor by the material of the envelope. When the envelopei consists of ordinary glass, platinum has'been found especially suitable for a leading-in conductor because of the'fact' thatit is practically non-oxidizable and-has a coeflicient of expansion which is'nearer to that of the glass than any other metal, and also because 40 platinum is wet by glass. Because of the reat cost of platinum,however, many ef orts have been made to secure a suitable substitute. ;It has b'eenrfound that ifgnickel and iron are alloyed in the proper propor-.

cations, a conductor may. be obtained which has the same coefiicient of expansion as glass.

- In attempting to use such aconductor in commercial practice, however, difiiculty has been experienced because of the large num-- ber of seals which are defective This is probably due to the fact that when 'sub 'jected t9 the heat-of the flame necessary for .sthe sealing-in operation an oxide poating is formed which is more or less porous and allows air to gradually leak-through between Y peratures.

between the'conductor and the glass than than that of. lead the glass and the conductor. It has also been found diflicult to prevent the formation of bubbles in the seal due to the liberation of gas from the conductor. or. the formation of gas by chemical reaction during the. sealing-in operation.

I have discovered, however, that there are certain metals whose oxides are readily soluble in glass at lamp seal making tem- Among these are cop r and cobalt and some of their alloys. (lfdinary lead lass, such as is'commonly used for incan escent lamps and rectifiers, has a coeflicient of expansion of about 8.8 x 10" while copper and cobalt have coeflicients of expansion of about 17 x 10' and 12 x 10" respectively. Hence, solid conductors-composed entirely of eithe of these metals are not commercially suitable for leading-in. conductors because of the great diiference between their coefiicients. of expansion and that of glass. By making a composite conductor, however, having a sheath of copper or cobalt and a core of metal having a lower coeflicient of ex ansion thanthat of glass, and by proper y proportionin the, relative thicknesses of the core an sheath, it

is possible to providea conductor, the total radial coefiicient of expansion of which is substantially the same as that of the glass with which it is tobe used. I have found that if such a conductor is used that there is an even better union in the cold state in the easeof platinum. In actual pTactice it has been found that by using my invention the number of defective seals has been reduced over 75% from the number commonly found when platinum employed. y y Most metals have a coefficient of expansion greater than that ofglass and hence cannot be used to form a core for the composite conductors. ,Amon those metals having a sufiiciently lowcoe cient-are tungsten and molybdenum, which have eoeificients of about 4.3 x 10" and 4.9 x 10* respectively.

There are, in addition to these metals, various alloys which can be readily prepared which have a coefiicient of expansion less (glass. For example, an

alloy of nickel an iron containing about 35% of nickel, has a coeificient of expansion fwhich is practically zero over a range of t ipperature from 0f to 100 C. -By vary- 11 ing the relative amounts .of nickel and iron,

it is possible jto .produceia'n alloy having any coeflicientd'esired between zero and that of nickel or iron; One, alloy whichI have used with satisfactory results contains from 53 to 55% of iron, from 44 to 46% of nickel, and from .75 to-1.25% of manganese, and 'not over.15% of carbon, .02%. of phoswhile the presence} of some of the impurities. apparently causes the "formation of bubbles. a

The coefficient ,of xpansion of the core material will. vary (:0 siderably with. differ-- ent lots of metal due to small variations in the proportions of the constituents and on thisaccount' it will be necessary in each case to measure the coeflicient of expansion of the core and sheath and the diameter of the core and from the values found calcu- -late the required thickness of sheath to give a finished conductor having substantially the K same coefii cient as the glass with which it is to be used; The lamp glass commonly used has a coefficient of expansionslightly below that of platinum One example of a compositeflwire suitable for such glass has a core of the above described nickel iron alloy containing 'about 44% nickel and a copper sheath of which the thickness ex.- pressed in-per cent o'fvthe diameter of the core is approximately6%, the approximate percentage of copper being about 20% by volume ofthe total volumeof the wire.

There are numerous ways in which the copper sheath may be applied to the core.

I prefer, however, to employ what I term the copper tube process. The alloy having the desired proportions-for the core is made up into rods. These rods as received from the rolling mill'are usually rough and not perfectly round, and may be polished or drawn throughdies togive them a smooth clean surface. They should then bethoroughly heat-treated at' a temperature of about1200 to1300 C. in an atmosphere of hydrogen or hydrogen diluted with nitrogen. The time 'of th1s heat treatment will depend "some whatupon the diameter ofthe rods; I havefound that when the rods of the particular alloy which I have men- 7 tioned' are about one-half inch in diameter prevents oxidation of the surface. In addifrom 8 to 10 hours isnecessary. After subjectingt h em' to the temperature mentioned for the desired period, I find it desirable to allow the'rods to cool slowly in a hydrogen or hydrogen-nitrogen atmosphere. This tioii toirenderin'g the .metal more easily I workable, this heat treatment also, prevents the forinationlof bubbles the glass when a seal is made.-- This is probably 'due to the fact that the hydrogen acting upon the heated alloy removes impurities such as carbon and possibly sulphur. I have found that if the heat treatment is continued until the rods contain no more than .02% of carbon, the tendencyof the sheathed wire to form bubbles is eliminated.

' It is essential that there should be a perfect union between the core and the sheath 7 of silver or brass. Before. applying the second coating the rods may be heated to the melting point of copper causing the thin I film of copper to'alloy with the-core metal. This insures a better stickin surface for the second coating. This secon coating, which may be plated on the rods or may be ap- "plied in the form of a thin sheet wound I around the rods, should preferably have a melting point below that of copper. After the rod has been heat-treated and coated in this way, a copper tube is selected having the required diameter and thiclmess. tube is slipped .over the core rod and made to fit tightly by drawing. The sleeved'rods are then placed ina furnace and heated under non-oxidizing conditions, preferably in hydrogen *or hydrogen: diluted with nitroge1i, to a temperature slightly above the melting point of thel silver or brass with which the cores are coated. The heated rods may then be run through rolls to insure a close union between the core and sheath.

Upon cooling the core and, sheath will be This found to be firmly soldered together. The;

rods thus prepared arethen ready to be' drawn into Wire according to. the usual methods, In drawing down to the desired size I find that itis desirable at frequent intervals, as, for example, .after eachreduction ofabout 40 nails in diameter, to anneal the wire for onehour at a temperature of aboutj900 (lin anon-oxidizing atmosphere, preferably hydrogen.- When pre pared in this way, the coeflicient of ex ansion of the finished annealed wire wil be found to be substantially the same as the value calculated and the adherence between used Zinc borate is especially suitable be; 130' f cause of the fact that it is non-hygroscopic and no special precautions are necessary for preserving the wire from moisture between the time when it receivesthecoating and the time it is used. The desired coating1 may be applied by passing the wire throng a solut1on.or suspension of the borate and then heating to a temperature suflicient to drive off all water from the coatin which adheres to the-wireand to thorougIily harden the coating. This coating serves a double purpose; t serves to protect the wire during the sealing-in operation and also facilitates v the solution or absorption of the oxide film by the glass. When a wire repared in this way is sealed into glass un er roper temerature conditions, a remarkab'y close aderence between the lass and the wire is obtained. Just why t 's is trueit is diflicult to state precisely. A-microscopic examination of such a seal, however, reveals the fact that. there is betweentheglass and the copper-sheath some material of difierent composition which apparently binds the two together. Thisbinding material may 2? be composed principally of the oxide which covers the wire but, from the fact which has been proved b ccareful experiment that it 'ssolve all of the oxide coating in the glass, it seems more probable that a portion at least of the oxide is dissolved in the glass and that the glass is more or less mingled with the remaining portion of the oxide, thus'producing a firm adherence between the glass and the oxide coating as well as filling the pores in the oxide. Whatever the composition of the binding 1nateri'al may be, it produces a more intimate union between the wire and the glass than in the case ofa platinum seal. This may be shown by crhshing both a seal made with platinum and a seal made with a composite wire pre ared as I have described. The glass wil break away cleanly Ton the platinum while small particles of the broken glass will be found adhering closely to the composite wire and particles of the coating of t e Wire will be found sticking to the glass that has beenv broken "away.

' would seem to indicate that the union between platinum and glass'is somewhat of the nature of a good mechanical joint while a wire such asyI have described will be so closely united to the glass that the two'cannot be separated without .tearing. The

* union between glass and platinum is not strong enoughto prevent a plain piece of platinum wire from being drawn through the glass after ithas been sealed in.

- In the accompanying drawing which illus- 6Q, trates my invention, Fig. 1 represents an. in-

. candescent lamp having a seal made in accordance with my invention, and-F g. 2 is a cross section, greatly magnified, of'a portion ofthe seal. As shown in the drawing the incandescent lamp has the usual leading-in making seals with platinum wire.

num wire where the" leading-in conductor passes through the. glass of the stem and for conductivity. In many cases it will be desirable to employ a similar, construction when the seal is made according to my inthe remaining portion ofthe conductor to- .use a wire of cheaper metalhaving good yention'. Because of .the comparative cheap- I ness of my wire, ho'wever,this will not be necessary from the standpoint of cost and it desired the entire leading-in conductor may, as-indicated in the drawing, be made of the wire which I have described. In case this construction is employed it may be desirable to increase the mechanical strength of the scal by nicking or bending or crimping, as indicated, that portion of the wire which passes through the glass of the stem.

When a section of a seal made in accordance with my invention is 'examined'microscopically it will be. found that ,the sheath 4 ofthe conductor, as illustrated in Fig. 2, is closelyjoined to the core 5 and that between the sheath and the glass body 6 there is a thin layer of binding material 7 which closely surrounds t e conductor and which seems to merge into t e glassi If the coeflicient of expansion of the wire 'is adjusted\ so that it is substantially the same as that of glass, the strains set up in the glass. when the seal is made will be reduced to a minimum. If, however, the wire employed has'a' greater coeflicient of expansion than ordinary glass, when the seal .cools Y th wire tends to shrink away from the glass and the union between the two is under tension. On the other hand if the coefficient of expansion of the wire-is materially less than that of glass the union between the glass and the wire when cooled will be under compression and there will be danger of the glass around the wire cracking."

The sealing-1n operation may be carried on with the apparatus ordinarily used for -While it has usually been considered necessary heretofore, when attempts have been madeto use an oxidizable wire, ,to carryon the sealing-in operation under non-oxidizing conditions I have found that such precautions are unnecessary with my composite wire and that the formation ofoxide on the surface of the wire appears to be of distinct advan tage instead of being detrimental. The sealing-in flames should of course be so adju sted that the temperature will be below the melting point of the copper or other metal of which the sheath is composed. I have found that in some cases when the temperature used approaches too closely the meltpoint of the'm'etal, all of the oxide on "a; wire is apparently dissolved in the glass or a platinum sheathedwire no difference isseals;

and that seals made'under such conditions are often' imperfect. may be caused by a; poor, adherence between the glass and the bare copper. of thesheath. On the other apparent between perfect and. imperfect .The conductivity of my composite wire may be made about two times that of pure platinum or three times that of commercial platinum and seven timesthat of nickel iron Wire having the same coeflicient of expansion. Hence. it is possible to use much smaller wires for a given current carrying capacity and thesmaller the wire used the easier it is to-niake perfect seals.

WhatI clainifas new and desire to secure by Letters Patent of the United States, is,.

1. An article of manufacturecomprising a vitreous body and-a composite wire sealed therein, said-wire having an outer sheath of qupreous metal with a thermal expansion higher than thatof said vitreous body and a core of metallicimateria'l with a thermal ex pansion lower than that of said vitreous body, said sheath and core being united and so proportioned that the'wire has a thermal expansion such'as to secure a seal with said vitreous'body.

2. .An article of manufacture comprising a body of vitreous material, andpa composite wire sealed therein, said wire being composed of a core of alloy containing nickel and 'iron, and a cupreous outer sheath of which the oxide is combined withfsaid vitreous'materialto form a thin layer of bind: ingmaterial firmly adherent to both-the wire and the vitreous material.

3. An article of manufacture comprising a vitreous body and a-wire-of substantially the samethermal expansion as said vitreous body hermetically sealed therein 'and surrounded by a thin composite" layer containing material from said'wire combined with i said vitreous body and firmly adherent to both said wire and said vitreous body.

ing athermal expansionlessf'than that of said glass, said wire and sheath being prof portioned to render the thermal expansion 4. An article of manufacture com-prising a body of glass, and a composite wire composed of a cupreousfsheath, and a' core havof'the-wire substantiallythe same as that of the glass, said wire being hermeticallysealed into said'body of glass and having a cer se orcherry red color Whereit is surrounded by the glass.

5. A composite low expansion wire com---i' prising a core of nickel steel and an-external copper sheathwelded thereto, said Wire as a whole having less expansion thanplatinum.

6. A composite low expansion wire comprising a core of nickel steel and an external sheath of a metal of the copper class i welded thereto, .said wire'as a whole having less expansion than platinum.

' 7. As a new article of manufacture, a copper surfaced wire havinga rate of expan: sion as a whele below that of platinum.

8. As a new article of manufacture, a com posite Wire havinga surface of-base metal and having a rate of expansion as a whole below that of platinum.

9. As a new article of manufacture, a

wire having a surface of metal of the copper class and a'rate of-expansion as a whole below that of platinum,

10. A 2-layer composite wire, one such layer being of low-expansion nickel steel and the other layer of high-expansion high-melting metal, the'wire as a whole having an expansion lessthan that of platinum.-

11. As'alainp wire, reinforced copper surface wire, said reinforcement consisting of an interior layer of low expansion nickeliron alloy.

12. As a lamp wire, a composite wire com-- posed of a layer of copper and another layer of low expansion nickel-steel insufficient amount'to reduce'the total expansion sufliciently to secure a seal with lamp glass.

13. A leading-in wire. comprising an outer sheath of high-melting,high-conductive material united to a core of nickel-steel having an average-coeflicient of expansion distinctly below that'of the sheath, the core being un der compression by the sheath at all temperatures to which the wire is subjected in lamp-making use.

14. The combination, with a gas-tight receptacle having a'wall of vitreous material,

of a composite leading-inwire sealed there- 1 111, said wire consisting of reinforced copper wire, said reinforcement consistin' of a layer of low-expansion nickel-iron a- 0y.

- 15. The combination, with ages-tight receptacle having a wall of vitreous material, of a composite leading-in wire sealed therein,'said wire being composed of a layer of copper and'another' layer of low-expansion nickel-steel in suflicient amount to reducethe total expansion of the composite wire sufliciently to secure a -seal with the glass.

' 16. The combination,- witha gas-tightre ceptacle having a wall of vitreous material, j

of a composite leading-inwire sealed therein, said wire having a surface sheath of highmelting base metal and a core of metallic material, the thermal expansion of the core and sheath being difierent and so proportioned as to produce a resultant expansion of the composite wire such as to'secure a seal with the glass.

17. The combination, with a gas-tight receptacle having a Wall of vitreous material, of a composite leading-in wire sealed therein, said wire having a surface sheath of copper and a core of metallic material, the thermal expansion of the core and sheath being difi'erent and so proportioned as to produce a resultant expansion of the composite wire such as to secure a seal with the glass.

In Witness whereof, I have hereunto set my hand this 21st day of January, 1915.

COLIN G. FINK. 

